As magnetic recording is pushed to higher areal densities, perpendicular recording offers advantages in thermal stability over longitudinal recording, thus delaying arrival at the super-paramagnetic limit. Another advantage of perpendicular recording with single pole (SP) head and perpendicular media, with a soft underlayer (SUL), is the ability to produce a larger write field than that of a ring head to record on relatively thick media with high anisotropy constant.
A typical read-write unit is illustrated in FIG. 1 which provides an ABS (air bearing surface) view of the assembly i.e. the unit as seen when looking directly up from the surface of the recording media. Shown in FIG. 1 are perpendicular magnetic write pole 11 and GMR (giant magneto-resistance) read head 12. Also shown, and of particular interest for the present invention, are three magnetic shields. Read head 12 is seen to be symmetrically disposed between shields 13 and 14 while write pole 11 is centrally located between shields 14 and 15.
Shields 13, 14, and 15 can serve as magnetic flux conductors for external fields which causes them to direct a certain amount of flux into the recording medium. When such a flux density is large enough, unwanted writing or erasing can occur. In particular, because of the magnetic softness of the shield materials, a small amount of external field can induce relatively large fields in the media and cause unintended erasure of information on the media.
In most current PMR designs the shields have a strictly rectangular shape as seen in FIG. 2. Due to the finite thickness and moment of the soft magnetic underlayer, flux distribution is not uniform over the surfaces of the shields. At sharp corners and edges, the flux density can be much higher than that at the shield center. In general, data under a shield corner will usually be erased first.
In application Ser. No. 11/117,672 filed Apr. 28, 2005, we disclosed a method and structure which greatly reduces a PMR head's sensitivity to stray field erasure, especially from shield corner field concentration. The basic principle disclosed there is to recess the corner from the ABS with an angle, shown as angle 31 in FIG. 3. This approach is pursued further In the present invention and a novel process is disclosed which allows excellent control of shield wall edge angle by post-lapping the ABS by means of ion milling.
In FIG. 4 we show the calculated dependence of maximum field in the media on the shield recess angle (in FIG. 3). The dimension of the shield in the calculation are 60 μm (W), 20 μm (L), and 4 μm (T). An external field of 200 Oe is assumed. As can be seen, the erasing field monotonically drops with reducing shield wall angle, the reduction being more pronounced when the wall angle is less 10 deg. However, creating such a small wall angle at wafer level poses great difficulties for current wafer processes. In the present invention we disclose a novel method to control the shield wall angle
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,198,597, Tateyama et al. disclose corner portions of the rear part of the magnetic pole recessed from the ABS by 0.05 microns or more by ion milling. An angle of 45 degrees is mentioned. In U.S. Pat. No. 6,742,241, Sasak, describes a light shield mask having an acute angle at the corner but this is not the same type of shield as that with which the present invention is concerned.